Early metastatic BRAFV600E mutation melanoma without known primary lesion: a case report.

INTRODUCTION AND IMPORTANCE: Malignant melanoma (MM) has a poor prognosis and is rare in China. CASE PRESENTATION: A 23-year-old man presented with an initial complaint of a mass under the left armpit without any symptoms. Multiple movable, merged, peanut-sized masses were found behind the left ear and a single peanut-sized mass in the left anterior chest and under the left armpit. These masses were medium-high in hardness upon palpation and were non-tender. Multiple black-brown flat moles, with diameters ranging from 2 to 4 mm, were observed on the anterior chest and abdomen; however, they did not meet any of the ABCD early diagnostic criteria for MM. Ultrasound revealed lymphadenopathy in the left neck and under the left armpit, with the mass under the left armpit subsequently excised. Histopathological results showed epithelioid cells with loosely arranged nuclei, melanin granules in the cytoplasm, and the following immunohistochemical markers: S-100 (+), HMB (partially+), Melan-A (+), SOX10 (+), P53 (locally+), and BRAFV600E mutation (+). Positron emission computed tomography (PET/CT) images revealed tumor metastases in multiple organs. After initiating treatment with Dabrafenib and Trametinib, the masses became smaller and fewer, with the one behind the left ear completely disappearing. DISCUSSION: It is rare to diagnose such an early metastatic BRAFV600E mutation MM without a known primary lesion in such a young man in China. PET/CT is effective for detecting MM locations, providing evidence for staging, evaluating and monitoring treatment effectiveness. Multidisciplinary diagnostic methods should be the best choice to confirm the diagnosis of MM. CONCLUSION: Dabrafenib and Trametinib can be used as a standard of care for advanced BRAFV600E melanoma.